How to change the standard communication device on android phone?

When I use aircall on my android phone, it always picks my Samsung watch as a speaker, and I have to switch it manually back every single time. It makes the usage pretty annoying, so I use it on the desktop mainly. I checked the settings, but I can not find how to switch it permanently. How to set up a standard communication device on an android phone, to block aircall from picking my watch as a speaker?